A crossword made of regular expressions: fill each cell so every row and column satisfies its own pattern clue.
Each row and each column carries a regex clue. Drop letters from a small alphabet into the grid so every line matches its pattern. A live matcher recolors each clue as you type, green when the line matches, amber while it is still satisfiable, red when no completion can work.
Slash Escape is a regex crossword that turns pattern-matching into a deduction puzzle, teaching regular expressions.
Row and column clues that are regular expressions make a grid puzzle out of pattern matching. The concept dates from the 1950s, when the American mathematician Stephen Cole Kleene formalised the regular languages; it reached everyday use through Unix text processing.
Every cell must satisfy both its row pattern and its column pattern at once, which is what makes the grid solvable rather than merely readable.
Intersecting constraints is the right way to learn regex, because the hardest part of the notation is reading it rather than writing it. A live matcher showing which lines currently pass turns an opaque expression into something you can probe.
Slash Escape is a regex crossword that turns pattern-matching into a deduction puzzle. It is an original, free browser game built in-house for PlayPendium.